1. Field of the Invention
The present invention relates to theatre lighting, and more particularly to controlling the temperature of lighting devices such as multi-parameter lights that include both optical and electromechanical components.
2. Description of Related Art
Theatre lighting devices are useful for many dramatic and entertainment purposes such as, for example, Broadway shows, television programs, rock concerts, restaurants, nightclubs, theme parks, the architectural lighting of restaurants and buildings, and other events. A multi-parameter light is a theatre lighting device that includes a light source and one or more effects known as xe2x80x9cparametersxe2x80x9d that are controllable typically from a remotely located console. For example, U.S. Pat. No. 4,392,187 issued Jul. 5, 1983 to Bohnhorst and entitled xe2x80x9cComputer controlled lighting system having automatically variable position, color, intensity and beam divergencexe2x80x9d describes multi-parameter lights and a central control system. Multi-parameter lights typically offer several variable parameters such as pan, tilt, color, pattern, iris and focus.
A multi-parameter light typically employs a light source such as a high intensity lamp as well as motors and other motion components which provide the automation to the parameters. These components are typically mounted inside of a lamp housing and generate large amounts of heat inside of the lamp housing, so that cooling by convection or forced air is required. The high intensity lamp generates the greatest amount of heat. However, motors used to automate the parameters also generate significant amounts of heat. Heat generation by the motors is a function of the number of motors within a lamp housing as well as the usage of the motors. Heat generation increases with increasing numbers of motors and with repetitive use in a high duty cycle. Various optical components such as filters, projection patterns, shutters, and an iris diaphragm are used within the lamp housing to collimate the light and focus patterns to be projected. These optical components are selectively moved in and out of the light path or controllably varied in the light path by motors to vary the attributes of the projected light, and generate varying amounts of heat as they interact with the light beam by reflection or absorption.
Many variables affect the internal temperature of the lamp housing of a multi-parameter light. For example, lamps provided by different manufactures may have differences in lumens per watt, or may have a spectral distributions that create more energy in the infrared spectrum thus further raising the internal temperature of the multi-parameter light. The optical components in the lamp housing that are used to vary the parameters lie in the path of the projected light. These components may reflect or absorb light. Light collimated or condensed by the optical components may be reflected back into the lamp housing, the components of the lamp housing, or the lamp itself, causing a rise in temperature of the lamp housing and its components. Light may also be absorbed by the optical components when placed in the path of the projected light. As these components absorb the condensed or collimated light, they generate heat and raise the temperature within the lamp housing. The ambient air temperature to which the instrument is exposed may also raise the internal temperature of the lamp housing from 25 to 40 Celsius. The position of the multi-parameter lamp housing also is a factor in the operating temperature, since the position may allow heat to rise in certain areas of the lamp housing. The motors within the lamp housing when used repetitively for shows or events that often repeat the change of a parameter may raise the temperature inside of the lamp housing and its components by 5 to 15 degrees Celsius.
Because of the presence of such substantial amounts of heat, some multi-parameter lights are constructed of various high temperature materials. For example, the insulation of the wiring to the lamp may be silicon or Teflon. The lamp housing of the multi-parameter light may be constructed of a high temperature polymer, which additionally helps to reduce the weight of the light and is often molded into a pleasing design shape. However, as the heat capacity of even these materials is not infinite, various cooling techniques are used. The most common cooling techniques are convection and forced air cooling. An example of a convection cooled multi-parameter light is the model Studio Color(copyright) 575 wash fixture, available from High End Systems, Inc. of Austin, Tex., URL www.highend.com. In this type of multi-parameter light, the convection cooled lamp housing contains the lamp, motors, optics and mechanical components, and is rotatably attached to a yoke that facilitates pan and tilt. The yoke is rotatably attached to a base, which contains the power supplies and control and communications electronics. See also U.S. Pat. No. 5,515,254, issued May 7, 1996 to Smith et al. and entitled xe2x80x9cAutomated color mixing wash luminaire,xe2x80x9d and U.S. Pat. No. 5,367,444, issued Nov. 22, 1994 to Bohnhorst et al. and entitled xe2x80x9cThermal management techniques for lighting instruments.xe2x80x9d An example of a forced air cooled multi-parameter light is the model Cyberlight(copyright) automated luminaire, available from High End Systems, Inc. of Austin, Tex., URL www.highend.com. In this type of multi-parameter light, the forced-air cooled lamp housing is stationary and contains all of the necessary operating components, including a positionable reflector to achieve the pan and tilt parameters.
Neither convection cooling nor forced air cooling is entirely satisfactory. Convection cooling is quiet but does not dissipate as much heat as forced air cooling. Forced air cooling typically is achieved with fans which increase the operating noise of the multi-parameter light.
A technique found both in forced air cooled multi-parameter lights and convection cooled multi-parameter lights for dealing with excessive heat in the lamp housing involves the use of a thermal switch to turn off the lamp when the temperature inside of the lamp housing exceeds specification, and then to turn on the lamp when the inside of the lamp housing falls back to a cooler temperature. FIG. 1 is a block diagram of a forced air cooled multi-parameter light which has a lamp housing 40. The lamp housing 40 contains various optical components such as a reflector 45, a lamp 46, a condensing lens 47, three filter wheels 48, 49 and 51, an iris diaphragm 50 (motor omitted for clarity), and a focussing lens 52 (motor omitted for clarity). The lamp housing 40 also contains a thermal switch 43, a lamp power supply 44, and a power supply 53 to power the lamp, various motors and electronics of the multi-parameter light. The electronics 41 within the lamp housing 40 include a communications node for receiving communication and command signals from a remote console (not shown) to vary the parameters of the multi-parameter light, and a microprocessor for operating the electromechanical system of motors (not shown for clarity) of the multi-parameter light as well as for turning on and off a fan 42 in accordance with the command signals. For cooling purposes, air enters the interior of the lamp housing 40 through a intake vent 54, and is drawn through the lamp housing 40 by the fan 42, and exits the lamp housing 40 through the fan and exhaust vent 42. The thermal sensor 43 is located next to the ventilation exit near the fan 42, and responds to the temperature at that point inside of the lamp housing 40 by opening the line power circuit if the temperature exceeds specification and closing the line power circuit when the temperature falls back into specification. If pan and tilt parameters are desired, a positionable reflector system (not shown) is provided after the focussing lens 52 and typically outside of the housing 40, although the reflector system may be located inside of the housing 40 if desired.
FIG. 2 is a block diagram of a convection cooled multi-parameter light which has a lamp housing 55. The lamp housing 55 contains many of the same type of components as the multi-parameter light of FIG. 1 (the component values may of course be different). The electronics 56 within the lamp housing 55 include a communications node for receiving communication and command signals from a remote console (not shown) to vary the parameters of the multi-parameter light, and a microprocessor for operating the electromechanical system of motors (not shown for clarity) of the multi-parameter light. Air enters the interior of the lamp housing 55 through a intake vent 58 which has cooling fins, and is drawn through the lamp housing 55 by convection currents and exits the lamp housing 55 through an exhaust vent 57 which also has cooling fins. The various cooling fins may be connected to various components in the lamp housing 55 to help dissipate heat from those components. The thermal sensor 43 is located next to the ventilation exit near the exhaust vent 57, and responds to the temperature at that point inside of the lamp housing 55 by opening the line power circuit if the temperature exceeds specification and closing the line power circuit when the temperature falls back into specification.
Another technique found in forced air cooled multi-parameter lights for reducing the heat generated by the lamp involves the use of a variable speed fan which runs at high speed to provide a great deal of heat dissipation when required but otherwise runs at lower speeds to achieve adequate cooling with reduced fan noise. FIG. 3 is a block diagram of a forced air cooled multi-parameter light which has a lamp housing 60. The lamp housing 60 contains may of the same type of components as the multi-parameter light of FIG. 1 (the component values may of course be different), except that a thermal switch is not necessarily present in the line voltage circuit. Instead, a thermal sensor 66 monitors the temperature at a point inside of the lamp housing 60 and furnishes the measurements to a sensor interface 65. The sensor interface 65 is part of the electronics within the lamp housing 60, which also include a communications interface 61 for receiving communication and command signals from a remote console (not shown) to vary the parameters of the multi-parameter light, and a microprocessor 62 for operating the electromechanical system of motors (not shown for clarity) of the multi-parameter light through a motor control interface 64 and for operating the speed of a variable speed fan 67 through a fan control interface 63. Air enters the interior of the lamp housing 60 through an intake vent 68, and is drawn through the lamp housing 60 by the variable speed fan 67 and exits the lamp housing 60 through the variable speed fan 67. The microprocessor 62 monitors the temperature within the lamp housing 60 and adjusts the speed of the fan 67 to maintain the temperature within the lamp housing 60 within specification. Fan speed may be set by the microprocessor 62 in various ways, such as, for example, by consulting a temperature-to-fan speed ratio table stored in local memory (not shown) to which the microprocessor 42 has access in a manner well known in the art.
If desired, a thermal switch such as the switch 43 (FIG. 1) may be added to the multi-parameter light of FIG. 3 to provide protection against overheating when the fan 67 is operating at full speed.
FIG. 4 is a block diagram of a forced air cooled multi-parameter light that has the same type of components as the multi-parameter light of FIG. 3, but has separate base and lamp sections with respective housings 70 and 71. The base housing 70 contains the communications interface 61, the microprocessor 62, the fan control interface 63, the motor control interface 64, the thermal sensor interface 65, the lamp power supply 44, and the motor and electronics power supply 53. The lamp housing 71 contains the thermal sensor 66, the reflector 45, the lamp 46, the condensing lens 47, the filter wheels 48, 49 and 51, the iris diaphragm 50, and the focussing lens 52. Various wires are run between the base housing 70 and the lamp housing 71 (some wires are omitted for clarity) through a wireway 73, which typically is a flexible conduit or a pathway between the bearings used to attach the lamp housing 71 to the base housing 70 on pan and tilt lights. Air enters the interior of the lamp housing 71 through an intake vent 74, and is drawn through the lamp housing 71 by the variable speed fan 72 and exits the lamp housing 71 through the variable speed fan 72. The microprocessor 62 monitors the temperature within the lamp housing 71 and adjusts the speed of the fan 72 to maintain the temperature inside of the lamp housing 71 within specification.
In the multi-parameter lights of FIGS. 3 and 4, an electronic circuit controls the fan speed in accordance with signals from a thermal sensor. As the temperature inside of the lamp housing rises, the sensor provides a signal to the electronic circuit that in turn increases the speed of the fan. This increased fan speed provides greater airflow and in turn lowers the temperature of the lamp housing and the components contained therein. While effective for temperature control, this solution is disadvantageous in settings where the ambient temperature is high and a high noise level is not acceptable. Such settings are quite common. For example, multi-parameter lights are often operated in groups in, for example, churches, theatres and television studios, where the ambient temperature in the vicinity of a group of lights may rise to above about 50 degrees Celsius. When the ambient temperature is high, the variable speed fan of a multi-parameter light operates near or at maximum speed and creates noise. Since several fans operating in close proximity at maximum speed create quite a lot of noise, forced air cooled multi-parameter lights are not entirely suitable for use at locations where a high noise level is not acceptable.
Convection cooled multi-parameter lights may be used where the noise of a forced air cooled multi-parameter light is unacceptable. However, convection cooled multi-parameter lights typically utilize lamps that generate less heat and are constructed of expensive high temperature materials.
For either convection cooled or forced air cooled multi-parameter lights, a thermal sensor or thermal cutoff switch may be employed to remove the supply voltage to the lamp if the temperature monitored by the sensor reaches a maximum allowable safe temperature. Unfortunately, this means that if the multi-parameter light is operated in high enough ambient temperatures, the lamp may shut down. It is possible that during a performance event with high ambient temperatures, one or more of the multi-parameter lights in the event may inadvertently shut down, causing great inconvenience and distraction.
Permitting a multi-parameter light to run too hot is not a good option. As the temperature of the lamp housing increases, the temperature of all the components in the lamp housing also increases. Typically, lamp life is shortened. The motors used for the automation can easily reach critical operating temperatures and sustain damage. Electronic circuitry if contained within the lamp housing, may reach operating temperatures that greatly shorten the life of components therein such as semiconductors, capacitors and transformers. Additional components and materials used for the construction and proper operation of the instrument and lamp housing may also be affected, such as polymers, elastomers and lubricants.
One embodiment of the present invention is a multi-parameter light comprising a housing, a variable power supply having an output and a control input, a lamp contained at least in part within the housing and coupled to the output of the variable power supply, a parameter actuator contained at least in part within the housing, a thermal sensor contained within the housing, and a control circuit having an input coupled to the thermal sensor and an output coupled to the input of the variable power supply.
Another embodiment of the present invention is a multi-parameter light comprising housing means, light source means contained at least in part within the housing means, means for actuating a parameter contained at least in part within the housing means, means for applying power to the light source means, means for operating the actuating means, means for monitoring temperature of the multi-parameter light, and means for adjusting power to the light source means when the temperature monitoring means indicates a temperature that is discrepant with a predetermined temperature specification to bring the temperature of the multi-parameter light back to the predetermined temperature specification.
A further embodiment of the present invention is a method of controlling the operating temperature of a multi-parameter light having a housing, a lamp contained at least in part within the housing, and at least one parameter actuator contained at least in part within the housing. The method comprises applying power to the lamp, operating the parameter actuator, monitoring the operating temperature of the multi-parameter light to obtain a sensor signal indicative of the operating temperature, and adjusting power to the lamp when the sensor signal is discrepant with a predetermined temperature specification to bring the operating temperature back to the predetermined temperature specification.